The synthesis of main group heterocycles such as boroles, galloles, siloles and phospholes via metallacycle transfer is well know to those who practice the art of pharmaceutical and pesticide research. A review of this chemistry is provided by Fagan et al in The Journal Of The American Chemical Society, 116, 1880-1889 (1994). The Group IV metallacycle compounds previously known have included substituted metallacycles with alkyl or silyl alkyl groups.
The use of main group heterocycles as ligands in organometallic complexes useful as olefin polymerization catalysts is disclosed by Sone et al in U.S. Pat. No. 5,434,116. Sone et al exemplify the use of catalysts having heterocyclic, phosphorus containing ligands ("phosphole" or "phospholyl" catalysts) which are activated by alumoxanes or certain "substantially non-coordinating anions", to produce polyethylene having a desirable molecular weight distribution-although these catalysts are not particularly active. Subsequent disclosures of the use of phosphole catalysts have been made in Patent Cooperation Treaty (PCT) application 95/04087 (deBoer et al, to Shell); European Patent Office (EPO) application 617,052 (Aoki et al, to Asahi) and EPO 741,145 (Katayama etal, to Sumitomo).
The use of alumoxanes and/or substantially non-coordinating anions as cocatalysts is well known to those skilled in the art of olefin polymerization and is typically associated with the use of so-called metallocene and/or half metallocene catalysts.
The combination of a metallocene catalyst (i.e. a catalyst having two cyclopentadienyl ligands) and an alumoxane cocatalyst is disclosed by Kaminsky etalin U.S. Pat. Nos. 4,404,344 and 4,542,199.
Hlatky and Turner subsequently made the important discovery that substantially non-coordinating anions may also function as cocatalysts for metallocene catalysts, as disclosed in U.S. Pat. No. 5,198,401. Other Hlatky and Turner patents of relevance to these cocatalysts include U.S. Pat. Nos. 5,153,157 and 5,407,884.
Half metallocene complexes (those with only one cyclopentadienyl ligand) have also been discovered to be versatile olefin polymerization catalysts.
Most notable is the bridged dianionic cyclopentadienyl-heteroatom ligand reported by Bercaw et al ("Bercaw ligand") at the Third Chemical Congress in North America (June 1988).
The use of a Group IV metal complex having a "Bercaw ligand" in combination with an alumoxane cocatalyst for olefin polymerization is disclosed by Canich in U.S. Pat. No. 5,055,438. Other patents which are relevant to the Bercaw ligand/alumoxane combination include U.S. Pat. Nos. 5,057,475; 5,096,867 and 5,227,440.
The use of a Group IV metal complex of the Bercaw ligand in combination with a substantially non-coordinating anion as a cocatalyst is disclosed by Stevens et al in U.S. Pat. No. 5,132,380. Other patents which are relevant to this catalyst/cocatalyst combination include U.S. Pat. Nos. 5,374,696 and 5,399,635.
The use of a metallocene or half metallocene in olefin polymerizations generally results in the production of polyolefins having both desirable properties (e.g. optical clarity, high impact strength, organoleptics) and undesirable properties (particularly poor processability, which is thought to be caused by the very narrow molecular weight distribution of most polymers produced this way).
An olefin polymerization catalyst which provides the desirable features of both the metallocene (or half metallocene) catalyst and the "phosphole" catalyst would represent a desirable addition to the art. [Conversely, an olefin polymerization catalyst which displays the undesirable features of both wou ld be nothing more tha n an academic curiosity!] The preparation of an organometallic complex having a simple cyclopentadienyl ligand and a simple heterocyclic ligand involves only trivial chemistry. Such organometallics have been prepared, tested, and reported to be comparatively uninteresting polymerization catalysts (see Janiak et al, Journal of Organometallic Chemistry 501 (1995) pp. 219-34).
The question whether a "bridged, divalent phosphole heteroatom ligand" (analogous to the Bercaw ligand) would be useful in the preparation of olefin polymerization catalysts was heretofore unanswered, perhaps because the use of conventional organometallic synthetic methods did not readily lead to the desired ligand.